mirror of https://github.com/python/cpython
187 lines
7.7 KiB
TeX
187 lines
7.7 KiB
TeX
\section{Built-in Module \sectcode{time}}
|
|
|
|
\bimodindex{time}
|
|
This module provides various time-related functions.
|
|
It is always available.
|
|
|
|
An explanation of some terminology and conventions is in order.
|
|
|
|
\begin{itemize}
|
|
|
|
\item
|
|
The ``epoch'' is the point where the time starts. On January 1st of that
|
|
year, at 0 hours, the ``time since the epoch'' is zero. For UNIX, the
|
|
epoch is 1970. To find out what the epoch is, look at \code{gmtime(0)}.
|
|
|
|
\item
|
|
UTC is Coordinated Universal Time (formerly known as Greenwich Mean
|
|
Time). The acronym UTC is not a mistake but a compromise between
|
|
English and French.
|
|
|
|
\item
|
|
DST is Daylight Saving Time, an adjustment of the timezone by
|
|
(usually) one hour during part of the year. DST rules are magic
|
|
(determined by local law) and can change from year to year. The C
|
|
library has a table containing the local rules (often it is read from
|
|
a system file for flexibility) and is the only source of True Wisdom
|
|
in this respect.
|
|
|
|
\item
|
|
The precision of the various real-time functions may be less than
|
|
suggested by the units in which their value or argument is expressed.
|
|
E.g.\ on most UNIX systems, the clock ``ticks'' only 50 or 100 times a
|
|
second, and on the Mac, times are only accurate to whole seconds.
|
|
|
|
\item
|
|
On the other hand, the precision of \code{time()} and \code{sleep()}
|
|
is better than their UNIX equivalents: times are expressed as floating
|
|
point numbers, \code{time()} returns the most accurate time available
|
|
(using UNIX \code{gettimeofday()} where available), and \code{sleep()}
|
|
will accept a time with a nonzero fraction (UNIX \code{select()} is
|
|
used to implement this, where available).
|
|
|
|
\item
|
|
The time tuple as returned by \code{gmtime()} and \code{localtime()},
|
|
or as accpted by \code{mktime()} is a tuple of 9
|
|
integers: year (e.g.\ 1993), month (1--12), day (1--31), hour
|
|
(0--23), minute (0--59), second (0--59), weekday (0--6, monday is 0),
|
|
Julian day (1--366) and daylight savings flag (-1, 0 or 1).
|
|
Note that unlike the C structure, the month value is a range of 1-12, not
|
|
0-11. A year value of $<$ 100 will typically be silently converted to
|
|
1900 $+$ year value. A -1 argument as daylight savings flag, passed to
|
|
\code{mktime()} will usually result in the correct daylight savings
|
|
state to be filled in.
|
|
|
|
|
|
\end{itemize}
|
|
|
|
The module defines the following functions and data items:
|
|
|
|
\renewcommand{\indexsubitem}{(in module time)}
|
|
|
|
\begin{datadesc}{altzone}
|
|
The offset of the local DST timezone, in seconds west of the 0th
|
|
meridian, if one is defined. Negative if the local DST timezone is
|
|
east of the 0th meridian (as in Western Europe, including the UK).
|
|
Only use this if \code{daylight} is nonzero.
|
|
\end{datadesc}
|
|
|
|
\begin{funcdesc}{asctime}{tuple}
|
|
Convert a tuple representing a time as returned by \code{gmtime()} or
|
|
\code{localtime()} to a 24-character string of the following form:
|
|
\code{'Sun Jun 20 23:21:05 1993'}. Note: unlike the C function of
|
|
the same name, there is no trailing newline.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{clock}{}
|
|
Return the current CPU time as a floating point number expressed in
|
|
seconds. The precision, and in fact the very definiton of the meaning
|
|
of ``CPU time'', depends on that of the C function of the same name,
|
|
but in any case, this is the function to use for benchmarking Python
|
|
or timing algorithms.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{ctime}{secs}
|
|
Convert a time expressed in seconds since the epoch to a string
|
|
representing local time. \code{ctime(t)} is equivalent to
|
|
\code{asctime(localtime(t))}.
|
|
\end{funcdesc}
|
|
|
|
\begin{datadesc}{daylight}
|
|
Nonzero if a DST timezone is defined.
|
|
\end{datadesc}
|
|
|
|
\begin{funcdesc}{gmtime}{secs}
|
|
Convert a time expressed in seconds since the epoch to a time tuple
|
|
in UTC in which the dst flag is always zero. Fractions of a second are
|
|
ignored.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{localtime}{secs}
|
|
Like \code{gmtime} but converts to local time. The dst flag is set
|
|
to 1 when DST applies to the given time.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{mktime}{tuple}
|
|
This is the inverse function of \code{localtime}. Its argument is the
|
|
full 9-tuple (since the dst flag is needed --- pass -1 as the dst flag if
|
|
it is unknown) which expresses the time
|
|
in \em{local} time, not UTC. It returns a floating
|
|
point number, for compatibility with \code{time.time()}. If the input
|
|
value can't be represented as a valid time, OverflowError is raised.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{sleep}{secs}
|
|
Suspend execution for the given number of seconds. The argument may
|
|
be a floating point number to indicate a more precise sleep time.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{strftime}{format, tuple}
|
|
Convert a tuple representing a time as returned by \code{gmtime()} or
|
|
\code{localtime()} to a string as specified by the format argument.
|
|
|
|
The following directives, shown without the optional field width and
|
|
precision specification, are replaced by the indicated characters:
|
|
|
|
\begin{tabular}{lp{25em}}
|
|
\%a & Locale's abbreviated weekday name. \\
|
|
\%A & Locale's full weekday name. \\
|
|
\%b & Locale's abbreviated month name. \\
|
|
\%B & Locale's full month name. \\
|
|
\%c & Locale's appropriate date and time representation. \\
|
|
\%d & Day of the month as a decimal number [01,31]. \\
|
|
\%H & Hour (24-hour clock) as a decimal number [00,23]. \\
|
|
\%I & Hour (12-hour clock) as a decimal number [01,12]. \\
|
|
\%j & Day of the year as a decimal number [001,366]. \\
|
|
\%m & Month as a decimal number [01,12]. \\
|
|
\%M & Minute as a decimal number [00,59]. \\
|
|
\%p & Locale's equivalent of either AM or PM. \\
|
|
\%S & Second as a decimal number [00,61]. \\
|
|
\%U & Week number of the year (Sunday as the first day of the
|
|
week) as a decimal number [00,53]. All days in a new
|
|
year preceding the first Sunday are considered to be in
|
|
week 0. \\
|
|
\%w & Weekday as a decimal number [0(Sunday),6]. \\
|
|
\%W & Week number of the year (Monday as the first day of the
|
|
week) as a decimal number [00,53]. All days in a new
|
|
year preceding the first Sunday are considered to be in
|
|
week 0. \\
|
|
\%x & Locale's appropriate date representation. \\
|
|
\%X & Locale's appropriate time representation. \\
|
|
\%y & Year without century as a decimal number [00,99]. \\
|
|
\%Y & Year with century as a decimal number. \\
|
|
\%Z & Time zone name (or by no characters if no time zone
|
|
exists). \\
|
|
\%\% & \% \\
|
|
\end{tabular}
|
|
|
|
Additional directives may be supported on certain platforms, but
|
|
only the ones listed here have a meaning standardized by ANSI C.
|
|
|
|
On some platforms, an optional field width and precision
|
|
specification can immediately follow the initial \% of a
|
|
directive in the following order; this is also not portable.
|
|
The field width is normally 2 except for \%j where it is 3.
|
|
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{time}{}
|
|
Return the time as a floating point number expressed in seconds since
|
|
the epoch, in UTC. Note that even though the time is always returned
|
|
as a floating point number, not all systems provide time with a better
|
|
precision than 1 second.
|
|
\end{funcdesc}
|
|
|
|
\begin{datadesc}{timezone}
|
|
The offset of the local (non-DST) timezone, in seconds west of the 0th
|
|
meridian (i.e. negative in most of Western Europe, positive in the US,
|
|
zero in the UK).
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{tzname}
|
|
A tuple of two strings: the first is the name of the local non-DST
|
|
timezone, the second is the name of the local DST timezone. If no DST
|
|
timezone is defined, the second string should not be used.
|
|
\end{datadesc}
|
|
|